Liquid-cooled mould

ABSTRACT

A liquid-cooled chill mold for continuous casting of thin steel slabs is disclosed whose cross-sectional length is a multiple of the cross-sectional width, having two opposing wide side walls, each with a copper liner and a backing plate, and narrow side walls delimiting the width of the slab, with the copper liners that delimit the mold cavity being detachably attached to the backing plates by metal studs made of a CuNiFe alloy and the metal studs being welded to the copper liners.

FIELD OF THE INVENTION

The present invention is directed to a liquid-cooled chill mold that isused for continuous casting of thin steel slabs whose cross-sectionallength is a multiple of its cross-sectional width.

BACKGROUND OF THE INVENTION

A liquid-cooled chill mold of the type in question is used forcontinuous casting of thin steel slabs whose cross-sectional length is amultiple of its cross-sectional width. At least each wide side wall iscomposed of a copper liner bordering the mold cavity and a steel backingplate. The copper liner is attached to the backing plate by metal studsprojecting laterally. The metal studs therefore pass through bore holesin the backing plate. At the ends of the bore holes are enlarged areaswhere nuts can be screwed onto the threaded ends of the metal studs.With their help the copper liner is tightened against the backing plate.

Within the scope of U.S. Pat. No. 3,709,286, it is known that the metalstuds may be made of stainless steel. However, metal studs made ofstainless steel yield poor welded joints with the copper liner becausecoarse-grained structures develop at the welds, which have a lowelasticity and therefore are very sensitive to flexural stresses.

From the Patent Abstracts of Japan JP-A 3258440, it is known thatthreaded bushings can be inserted into rear bore holes in the copperliner bordering the chill mold space, and longer rods passing laterallythrough a cooling box can be screwed into these bushings, and the copperliner tightened against the stainless steel backing plate. To do so,bore holes are also provided in the backing plate. In addition, shortfastening studs are attached to the rear side of the copper liner bystud welding. These sort fastening studs are provided with bushings intowhich the rods passing through the cooling box can be screwed.

Against the background of this related art, the object of the presentinvention is to create a liquid-cooled chill mold for high castingrates, in particular for continuous steel casting in close-to-finaldimensions, with a great reduction in strength problems in areas wherethe metal studs are joined to the copper liners.

SUMMARY OF THE INVENTION

The object of the present invention is achieved with a liquid-cooledchill mold for continuous casting of thin steel slabs whosecross-sectional length is a multiple of the cross-sectional width,having two opposing wide side walls, each with a copper liner and abacking plate, and narrow side walls delimiting the width of the slab,with the copper liners that delimit the mold cavity being detachablyattached to the backing plates by metal studs made of a CuNiFe alloy andthe metal studs being welded to the copper liners.

At the core of the present invention is the measure of producing themetal studs specifically of a CuNiFe alloy. Because of such metal studs,in particular hard-drawn metal studs, a considerable increase instrength is achieved with only a narrow scattering in strength in thewelded joints with the copper liner. The latter may be made of purecopper, e.g., SF--Cu (oxygen-free copper ASTM C12200), or a copper alloywith a high temperature stability, e.g., a hardenable copper alloycontaining chromium and/or zirconium additives. This eliminates thepreviously unreliable handling and the many influencing factors duringwelding which entail 100% testing.

In an especially advantageous embodiment, the metal studs are made of aCuNi30Mn1Fe material.

To attach the metal studs to the copper liners, the essentially knownstud welding method is used to advantage.

To improve the strength and toughness of the welded joint, the metalstuds are welded to the copper liners using a filler material.

Nickel is used in particular as a filler material here. The fillermaterial may be applied as a thin plate between the metal studs andcopper liners. It is likewise possible to provide the copper liners withfiller material at the connecting points or to plate the end faces ofthe metal studs. Furthermore, it is possible to use nickel rings aroundthe periphery of the metal studs as filler material.

In another embodiment of the basic idea of the present invention, copperliners for the wide side walls have groove-like coolant channels runningparallel to the casting direction and covered by the backing plates.With the help of such coolant channels, an increased transfer of heatfrom the casting side to the cooling water can be guaranteed, so thathigh casting rates can be achieved. Cracking in the copper liners anddamage to any surface coatings that might be present are eliminated.Coolant channels in the copper liners are used in particular when thecopper liner is thick enough to allow coolant channels with asufficiently large cross section to be formed.

To also dissipate heat intensively in the area of the metal studs, thecopper liners have cooling holes running next to the coolant channelsand parallel to the casting direction, extending in the verticalcross-sectional planes of the metal studs. Such cooling holes can beproduced by mechanical drilling. Coolant transferred through thesecooling holes prevents a local rise in temperature in the copper linersaround areas where the metal studs are connected to the copper liner inthe continuous casting operation.

The cooling bores are preferably arranged in the area of the bath level.

When using thin copper liners which guarantee a very good heat transfer,the present invention proposes that the backing plates have groove-likecoolant channels running parallel to the casting direction and coveredby the copper liners. Then no coolant channels are provided in thecopper liners. A combination of coolant channels in the copper linersand in the backing plates may optionally also be used.

To further increase the casting rate, the cross section of the moldcavity is designed with larger dimensions at the pouring end than at theoutlet end.

In this connection, it is also advantageous if the mold cavity has amultiple conicity.

As used herein, the phrase multiple conicity refers to a mold havingsidewalls with different tapers in different sections of the mold. Inorder to achieve optimal solidifying conditions for the molten metal inthe chill molds, the chill molds must be conically tapered in thecasting direction due to the shrinkage of the casting shell upon itsformation. In this case, the conicity is a function of the speed and thetype of the steel to be cast. Instead of the customary linear conicityused up to this point, chill-mold geometries having two-stage,three-stage, multi-stage, or parabolic conicities are now used inadjusting to the shrinkage of the respective steel melt. If three lengthsections of the chill mold cavity, e.g. the pour-in area, the middle,and the extrusion outlet, each have different degrees of conicity, thisis referred to as three-stage conicity.

Finally, a flared end tapering in the casting direction may be providedon the pouring end of the mold cavity. This flare serves to accommodatea submerged tube in particular.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in greater detail below on the basisof embodiments illustrated in the drawings, which show:

FIG. 1 shows a diagram of a vertical longitudinal section through aliquid-cooled chill mold;

FIG. 2 shows an enlarged partial view of the back side of a copper linerof the chill mold in FIG. 1 according to arrow II in FIG. 3;

FIG. 3 shows a partial horizontal section through a wide side wall ofthe chill mold in FIG. 1 on an enlarged scale;

FIG. 4 shows a partial horizontal section through a wide side wallaccording to another embodiment, also on an enlarged scale;

FIG. 5: a diagram of a vertical longitudinal section through aliquid-cooled chill mold with multiple conicity.

DETAILED DESCRIPTION

FIG. 1 shows a liquid-cooled chill mold 1, which is illustrated only indiagram form, for continuous casting of thin steel slabs (not shown)whose cross-sectional length is a multiple of its cross-sectional width.Chill mold 1 has two opposite multilayer wide side walls 2 and twonarrow side walls 3, also opposing one another, forming mold cavity 4.

On pouring end 5 of mold cavity 4, wide side walls 2 are provided withflared sections 6 which taper smoothly toward the bottom along part ofthe height of chill mold 1. The cross section of mold cavity 4 isrectangular at slab discharge end 7 and is based on the desired crosssection of the thin slab. The purpose of the two opposing flaredsections 6 is to create space required for a submerged tube (not shown)for supplying the molten metal.

As FIG. 3 also shows, each wide side wall 2 has a copper liner 8bordering mold cavity 4 and a steel backing plate 9. Groove-like coolantchannels 10, which can be supplied with cool water, run parallel tocasting direction GR, and are covered by backing plate 9, are providedin copper liner 8, as also indicated in FIG. 2, which does not showbacking plate 9.

In addition, FIGS. 2 and 3 show that cooling holes 11 which can alsoreceive cooling water run parallel to coolant channels 10. Cooling bores11 run in vertical cross-sectional planes QE of metal studs 12 made ofCuNi30Mn1Fe, which are attached to rear side 14 of copper liner 8 by thestud welding method using nickel rings 13 as filler material. Metalstuds 12 pass through bore holes 15 in backing plate 9. By screwing nuts16 onto threaded ends 17 of metal studs 12, copper liner 8 is tightenedonto backing plate 9 and secured there. Nuts 16 sit in enlarged endsections 18 of bore holes 15.

Coolant is supplied to cooling holes 11 through coolant channels 10,expediently through a branch 19 between a cooling hole 11 and adjacentcoolant channel 10, as shown in FIG. 2.

FIG. 3 also shows that coolant channels 10 next to cross-sectionalplanes QE of metal studs 12 are deeper than the other coolant channels10.

Coolant channels 10 and cooling holes 11 are arranged in a copper liner8 if copper liner 8 has a sufficient thickness D.

However, if a thinner copper liner 8a is used, coolant channels 10a areincorporated into backing plate 9a according to FIG. 4 and are coveredby copper liner 8a as copper liner 8a is secured to backing plate 9awith metal studs 12.

What is claimed is:
 1. A liquid-cooled chill mold for continuous castingof thin steel slabs whose cross-sectional length is a multiple of thecross-sectional width, having two opposing wide side walls, each with acopper liner and a backing plate, and narrow side walls delimiting thewidth of the slab, with the copper liners that delimit the mold cavitybeing detachably attached to the backing plates by metal studs made of aCuNi30Mn1Fe alloy and the metal studs being welded to the copper liners.2. The chill mold according to claim 1, characterized in that the metalstuds are attached to the copper liners by stud welding methods.
 3. Thechill mold according to claim 1, characterized in that the metal studsare welded to the copper liners using a filler material.
 4. The chillmold according to claim 3, characterized in that the filler material isnickel.
 5. The chill mold according to claim 1, characterized in thatthe copper liners of the wide side walls have groove-like coolantchannels running parallel to the direction of casting and covered by thebacking plates.
 6. The chill mold according to claim 1, characterized inthat the copper liners have cooling holes running parallel to thecasting direction in addition to the coolant channels and extending inthe vertical cross-sectional planes of the metal studs.
 7. The chillmold according to claim 6, characterized in that the cooling holes arearranged in the area of the bath level.
 8. The chill mold according toclaim 1, characterized in that the backing plates have groove-likecoolant channels running parallel to the casting direction and coveredby the copper liners.
 9. The chill mold according to claim 1,characterized in that the cross section of the mold cavity is larger atthe pouring end than at the slab discharge end.
 10. The chill moldaccording to claim 1, characterized in that the mold cavity has amultiple conicity.
 11. The chill mold according to claim 1,characterized in that the mold cavity has at least one flared section atthe pouring end, tapering in the casting direction.